2n5457 alternative

[peterg]

Are ECG 312, NTE 451, MPF 102 or 2N5951 subs for 2N5457?

[Kipper4]

i'm certain about the mpf 102 also j201's check the data sheets.
Google's you friend, Search: 2N5457 substitute

[smallbearelec]

Probably, though the specs for the NTE and ECG are notorious for being very broad. If you need specific types of genuine, branded parts at a reasonable price, we have good stock.

http://www.smallbearelec.com/servlet/Categories?category=Transistors%2C+FETs+%26+MOSFETs

Regards
SD

[peterg]

Thanks. Its for a Boss Slow Gear

[midwayfair]

Thanks. Its for a Boss Slow Gear

2sk30 mind the pin out. 2n5952, put in backwards.

If it's a buffer, literally any FET will work.

[Buzz]

I've subbed a 2n5484 in the past. Worked fine.

[duck_arse]

avoid the j201 for the slow gear, try the mpf102, which may have a too-high Vgs, or the 2n5457, 2n5486, mpf105, mpf106 or bf245A or bf245B. I found the higher-current fets work better in this circuit. test everything you can get yr hands on, basically.

[Kipper4]

Transistor roulette.

[peterg]

Thanks All.

I went out and bought some 2n5457s to compare with what I had on hand. The sweetish spot on the trim pot was the tail end on one side and I may not have been able to hit the optimum position. I ended up with an mpf102 or a 2n5951. Not sure which since they aren't branded and where in a bag marked with both names. Had a truck load from a phase 45 project.   

Kipper4 - transistor roulette it was!

[brett]

Hi
just for future reference to this thread:

If it's a buffer, literally any FET will work.

No. If the Vgs(on/off) is too high, there might not be enough headroom to keep the JFET on.

i'm certain about the mpf102 also j201's

If you mean certain that they are NOT like the 2N5457, then I agree. J201 is one end of the Vgs(on/off) spectrum (very high, -one volt), and MPF102 is the other end (very low, -several volts). Transconductance is proportional to Vgs, so potential gain varies too, making any amplifier circuit behave differently with different JFETs.
cheers

[midwayfair]

Hi
just for future reference to this thread:

If it's a buffer, literally any FET will work.

No. If the Vgs(on/off) is too high, there might not be enough headroom to keep the JFET on.

There are FETs that don't work as a basic source-follower? Like what?

[R.G.]

For general use, the 2N5485 is a good choice. It's Vgsoff is about 2-3V, and very useful in 9V powered applications.

There are FETs that don't work as a basic source-follower? Like what?

That's no what he said. What he said was there might not be enough headroom.

A JFET gate must be biased at some lower voltage than the source (for N-channel devices, reverse for P-channel) for it to work properly. This voltage will be something smaller than Vgsoff, and will vary depending on what current is needed to get the device biased where you want it, the Idss of the device, and the transconductance of the device.

A JFET with a Vgsoff of 1V or less like the J201 will have the source less than 1V more positive than the gate. So if you use it in self-bias with the gate grounded through a 1M or so, the source will be at something less than 1V. If you have an MPF102, the datasheet says it has an active Vgs of -0.5 to -7.5V. So you may get a device where it will bias properly with the gate held at ground and the source up at 7.5V in the self bias setup. Or the source may be at 0.5V. Can't tell, so you have to pick devices.

Obviously, for a follower to have maximum undistorted swing, you want the source near the middle of the power supply. You'd like a device with a Vgs in the active region of about 4-5V. Too low (1V, say) and you cut off the swing by bumping into ground. Too high (7.5-8V) and your follower bumps into the power supply.

They'll work as source followers. But there are different definitions of "work".   

[Kipper4]

read the bottom of this post to see how RG explained what i was doing

http://www.diystompboxes.com/smfforum/index.php?topic=103041.0

[bushidov]

So, with that being said, would a J211-D74Z work in place of a 2N5457, when used in a pedal as a follower? It's VGS Off min is 2.5V while it's max is 4.5V. I noticed that the 2N5485, min/max for VGS Off is 0.5V to 4.0V. The 2N5457 is 0.5 to 6.0V. I am wondering if the J211's VGS Off range is too thin (only 2 volts) to do that job well. I was also looking at the BF256B, which min/max is 0.5 to 8.0V, but that makes me wonder if it will get to close to ground or supply, as explained in the above explanation from RG

[ElectricDruid]

Transistor roulette.

The house always wins...

[reddesert]

So, with that being said, would a J211-D74Z work in place of a 2N5457, when used in a pedal as a follower? It's VGS Off min is 2.5V while it's max is 4.5V. I noticed that the 2N5485, min/max for VGS Off is 0.5V to 4.0V. The 2N5457 is 0.5 to 6.0V. I am wondering if the J211's VGS Off range is too thin (only 2 volts) to do that job well. I was also looking at the BF256B, which min/max is 0.5 to 8.0V, but that makes me wonder if it will get to close to ground or supply, as explained in the above explanation from RG

Those V_gs (off) values are tolerances, that is they tell you the range of values to expect in a sample of FETs labeled J211 or 2N5457 or whatever. A single device has one value of V_gs(off).

The source follower application isn't too critically dependent on JFET parameters as long as you can get it to bias somewhere in the middle of your 9V supply as RG explained. So if you had a bag of BF256B that are speced to have V_gs (off) between -0.5 and -8.0V, it's likely that some of them would work, but if there are any that have V_gs(off) around -7 or -8V, they might not work as desired. That's basically what RG said, above.